It is known, for example from my U.K. Pat. No. 1,532,995, to mount the plates to a supporting surface by means of a pair of elongate mounting members spaced apart and extending parallel to each other and at right angles to the plates, the mounting members having a series of pairs of ribs adapted to co-operate with the rearward flanges of the plates so that the plates are a resilient push fit on the mounting members, the width of the plates between their flanges being a multiple of the unit centre-to-centre spacing of adjacent pairs of ribs so that different widths of plates can be mounted to the same mounting members. Separate end closure members for the plates can also be provided to give a neat finished appearance. The present invention seeks to simplify this arrangement and the equipment necessary when a plate of predetermined width is to be mounted to a support.